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Drinking Water

Trihalomethanes in Drinking Water

Trihalomethanes (THMs) are a group of compounds that can sometimes be found in chlorinated water that is drawn from a source with high levels of organic materials. THMs are produced when chlorine reacts with the naturally occurring organics in the source water. The health risks from drinking water that has not been disinfected are much higher than the perceived risks from disinfection by-products, including THMs.
Drinking water is carefully treated and monitored by the operator, the Ministry of the Environment, Conservation and Parks as well as the health unit, to ensure it meets water quality standards. According to the Canadian Drinking Water Guidelines and the Ontario Drinking Water Quality Standards, the maximum acceptable concentration for THMs is a running annual average of 100 µg/L.
Chlorine is routinely used for drinking water disinfection because it is a very effective way to reduce bacteria, viruses and parasites. Chlorine also helps to reduce bacterial regrowth, biofilm formation and recontamination of water as it travels from the treatment plant to your home. The use of chlorine in the treatment of drinking water has virtually eliminated waterborne diseases because chlorine can kill or inactivate most micro-organisms commonly found in water. The majority of drinking water treatment plants in Canada use some form of chlorine to disinfect drinking water. The success of chlorine use in Canada today can be measured by the dramatic reduction of waterborne diseases such as Typhoid fever, cholera and dysentery.

Chlorine is important in drinking water treatment for controlling pathogenic organisms that can make us sick. Drinking water that is disinfected with chlorine to kill bacteria and viruses such as E. coli and cholera, is a benefit that far outweighs the perceived negative health risks at the present time.

Research shows there are no established adverse health effects associated with short-term variations in THM concentrations, however, continued research is required to further understand the potential association between THMs and adverse health outcomes.

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